Mammalian newborns maintain proximity to their parents or a home nest for care and protection but as they mature and gain independence, they must explore their environment to learn of its resources and dangers. This transition from dependence to independence is facilitated by the emergence of a motive to explore novel places during weaning. This transition is critical to adult independence in many species and a failure to complete it may result in difficulty negotiating unfamiliar environments in adulthood. Indeed, studies of human infants have shown that difficulty coping with parental separation can predict adult disorders like agoraphobia and panic disorder, disorders associated with excessive anxiety about leaving a familiar place. The neurohormonal factors that are responsible for the developmental emergence of the exploratory motive, a critical component of the transition to adult independence, are poorly understood. This research proposal investigates the developmental emergence of this motive in the rat. The central hypothesis of this proposal is based on several findings. First, research in adult rats has shown that behavioral responses to novel places are dependent on nucleus accumbens (NAc) dopamine activity. Second, the motive to leave the home nest and explore novel places emerges during the third postnatal week. The central hypothesis of this proposal is that an age-dependent enhancement of novelty-evoked accumbens dopamine activity facilitates exploratory behavior during the third postnatal week. To test this hypothesis studies are proposed which will 1) determine whether novel contexts evoke an age-dependent increase in NAc dopamine activity and 2) determine whether age-dependent changes in exploratory behavior are dependent on NAc dopamine release.